This invention relates to structural members, such as beams, wooden trusses, etc., which include a wooden chord member extending along the length of the structural member and a multi-layered laminated wooden web, such as a plywood web, joined along an edge of the web to the chord member. In a structural member such as an "I" beam, two of such chord members extend along opposite edges of the beam and the web described spans these chord members and is joined along opposite edges to each.
Generally, an object of the invention is to provide an improved construction for such a structural member which results in enhanced load-bearing characteristics in the member.
More particularly, the invention concerns a novel construction for the multi-layered laminated wooden web present in the member, and the joint of such web with the chord member, which results in improved load-bearing characteristics in the member as a whole.
A structural member or beam constructed pursuant to the invention includes what is referred to herein as a strongback layer forming one face of the web in the beam, with grain extending perpendicular to the grain of the chord member to which the web is joined. Also part of the web is another layer forming the opposite face of the web, with grain extending in the same direction, and one or more core layers or laminas with grain paralleling the grain of the chord member. The thickness of the strongback layer is greater than the thicknesses of other layers in the web having similar grain direction. Furthermore, the edge of the web, where such is joined to the chord member, is shaped so that the strongback layer protrudes beyond other layers in the web to form a ridge extending along the web's edge.
The chord member has a groove extending therealong receiving the edge of the web having a cross-sectional profile which corresponds to the cross-sectional profile of the web's edge. Thus, the groove described has a portion of greater depth receiving the ridge formed by the protruding edge of the strongback layer, and a portion of lesser depth receiving the margins of one or more intermediate core layers and the other face layer in the web. In joining the web edge to the chord member, an adhesive bond is provided over all exposed surfaces of the strongback layer as well as over portions of the opposite face layer in the web which is received within the groove of the chord member.
Preferably, the web is positioned relative to the chord member whereby a plane bisecting the chord member and paralleling the faces of the web is offset toward the strongback layer of the web from a plane paralleling the web faces which bisects the web. This offset serves to transfer a greater loading to the strongback layer in the web then were the web to be truly centered relative to the chord member.
With the construction described, a superior adhesive bond is formed between the chord member and vertical grain surfaces of the web (i.e., surfaces of the web with grain extending perpendicular to the grain of the cord member), and thus there is optimal uniting of the chord member to portions of the web which withstand deflection of the chord member with the structural member under load. There is full core integrity between various layers of the web which are joined to the strongback layer, unlike dovetail joints known in the art which have core layers terminating inwardly of opposite face layers bonded to the core layer. Webs may be constructed with the strongback layer having grain which extends perpendicular to the grain of the chord of one grade, and other layers of like grain direction of a lesser grade, with structural members produced therefrom meeting accepted industry standards, offering an opportunity for enhanced utilization of available wood supplies.
Manufacture of the structural member of the invention is performed relatively easily. The groove in the chord member which receives the edge of the web is readily prepared using conventional milling equipment. Placement of the edge of the web within the groove is a simple operation performable with little chance of inadvertent damage to the materials being handled.